Interface Location

[AnthonySterling]

Probably very obvious, but it's late and I'm having a little session of "alcohol fuelled development" but could someone explain why I'm receiving the error:-

Fatal error: Can't inherit abstract function EnglishBreakfast::hasHashBrowns() (previously declared abstract in NorthernBreakfast) in C:\webroot\www\f.php on line 17

<?php
interface EnglishBreakfast
{
    public function getBeans();

    public function getBacon();

    public function getSausage();

    public function getEggs();

    public function getToast();

    public function hasHashBrowns();
}

abstract class NorthernBreakfast implements EnglishBreakfast
{
    abstract public function hasHashBrowns();

    public function getBeans()
    {
        return 'Heinz';
    }

    public function getBacon()
    {
        return 'Danish Back';
    }

    public function getSausage()
    {
        return 'Cumberland';
    }

    public function getEggs()
    {
        return 'Scrambled';
    }

    public function getToast()
    {
        return 'Dark, both sides, dry';
    }

    public function hasBlackPudding()
    {
        return true;
    }
}

class SilversBreakfast extends NorthernBreakfast
{
    public function hasHashBrowns()
    {
        return 'of course!';
    }
}

class Meals
{
    protected $aMealsToday = array();

    public function setBreakfast(EnglishBreakfast $oBreakfast)
    {
        array_push($this->aMealsToday, $oBreakfast);
    }
}

$oMeals = new Meals();

$oMeals->setBreakfast(new SilversBreakfast());
?>

Surely it must be possible for an object to implement an interface whilst leaving a child object to fulfil an abstract method, even moving the declaration of the interface implementation to the child object fails with the same error.

Should I just stop coding and go to bed?

[styloa]

Out of interest.... what exactly were you drinking? I'm going to get some ice and pour a bit of Bells over it. Might help read that yummy code of yours

[AnthonySterling]

Off Topic:

Maybe it will, currently Vodka from the freezer. Mrs.SilverBulletUK is out with the girls tonight so I get to sing to bad 80's music, code bad PHP and no one will know!

[crmalibu]

Damn you and your breakfast with bacon posts...make me hungry lol

If you think about it, there's no reason you would want/need to declare the method signature again in NorthernBreakfast at all unless you actually implement it. You can't change the signature, so either you just inherit the abstract method and let a subclass provide the implementation, or you provide the implementation there.

So long as the class is abstract, you don't need to provide implementations for any inherited abstract methods(all the stuff from your interface).

[AnthonySterling]

I do like bacon. *Homer Simpson style drool*

I found a presentation by Udi Dahan where he indicates, for maximum flexibility, you code to interfaces throughout the whole application.

Every object has an interface and, where composition is used, accepts any object which implements a specific interface.

I doubt this is ground breaking, it makes far too much sense not to be, but I've never approached building application in this method so thought I'd give it a go.

I was trying to figure out a way to have a base object which MUST be extended, this object would implement an interface which would be required in another object.

You hit the nail on the head crmalibu and pointed me in the right direction, cheers! I think it was case of 'not being able to see the forest for the trees'.

Here's the non-bacon related way I did it.

<?php
interface ISwitchable
{
    public function switchOn();

    public function switchOff();
}

class RemoteControl
{
    public function addSwitchableDevice(ISwitchable $oDevice)
    {
    }
}

abstract class BaseTV
{
}

class ImprovedTVWithSwitch extends BaseTV implements ISwitchable
{
    public function switchOn(){}

    public function switchOff(){}
}

$oRemote = new RemoteControl();

$oRemote->addSwitchableDevice(new ImprovedTVWithSwitch());
?>